BackgroundHemoglobin A1c (HbA1c) levels are low in patients with hemolytic anemia, as HbA1c reflects mean erythrocyte age (MRBC). Erythrocyte creatine (EC) is a hemolytic indicator that also reflects MRBC. We previously reported an equation for estimating MRBC using EC (EC‐MRBC).AimsIn this study, EC‐MRBC was compared to the HbA1c level expressed in the International Federation of Clinical Chemistry and Laboratory Medicine units (iA1c) and to the iA1c/glycated albumin (GA) ratio to estimate MRBC.MethodsThis study included 238 subjects, including patients with hemolytic anemia and/or type 2 diabetes mellitus (T2DM).ResultsIn non‐diabetic individuals, both iA1c and iA1c/GA showed a strong positive correlation with EC‐MRBC (p < 0.0001). The equations to estimate iA1c‐MRBC and iA1c/GA‐MRBC derived from the regression equations between EC‐MRBC and iA1c, and EC‐MRBC and iA1c/GA in nondiabetic individuals were 1.45 × iA1c and 20.0 × iA1c/GA, respectively. iA1c‐MRBC and iA1c/GA‐MRBC in non‐diabetic individuals without hemolytic anemia were 57.6 ± 4.0 and 57.1 ± 6.4 days, respectively, and iA1c/GA‐MRBC in T2DM patients without hemolytic anemia was 56.0 ± 8.8 days.; no significant difference was seen in the comparisons.ConclusionsThe MRBC can be estimated using iA1c or iA1c/GA in non‐diabetic individuals, and iA1c/GA in T2DM patients.